The purpose of this project is to study the mechanism of tyrosine hydroxylase (TH) induction in glomus cells of the carotid body. Exposure to hypoxic conditions causes an initial selective decrease in the dopamine concentration and a long-term increase in TH activity. Since the increase in TH activity can be abolished by cycloheximide increased protein synthesis appears to be involved. Blockade of TH-induction by trans-section of the carotid sinus nerve proposes the existence of a reciprocal synapse between glomus cell and sinus nerve terminal.